The invention relates to an apparatus for liquid delivery, in particular into a chemical vapour deposition CVD installation, or into a chemical vapour reaction reactor, comprising:
an inlet head equipped at least with one injector or spray nozzle having an inlet for delivery of liquid precursors or precursors in solution,
a control circuit to periodically inject droplets of preset volume of the liquid precursors or a continuous or pulsed aerosol flow into an evaporation chamber,
injection means for injecting a vector gas into said evaporation chamber,
heating means designed to heat the evaporation chamber to achieve the change of liquid/vapour state of the liquid precursors, or of the solvent and precursor mixture,
and an outlet tube designed to send the vaporised injected precursors to a reactor.
The CVD reactor is generally equipped with a pumping system or with a vent to create a vapour flow to the reactor.
The document FR-A-2,707,671 describes a process and apparatus for delivery of precursors into a chemical vapour deposition CVD enclosure. The deposition enclosure is divided into two parts by a porous material. The upper part constitutes the evaporator and the lower part at higher temperature forms the deposition chamber. The porous separator is made of steel wool, which lets the gas flow, and any droplets which have not been vaporised by the evaporator, pass. It is however of paramount importance in CVD processes that the whole of the injected liquid be evaporated before entering the deposition chamber.
The document WO 96 20897 describes an evaporator equipped with several channels filled with beads made of glass, metal or ceramic. When the liquid flows in the channels, it comes into contact with these beads which form obstacles.
The object of the invention is to achieve an improved evaporation apparatus enabling optimum volatilisation of the liquid precursors or precursors in solution to be obtained after the injection phase, and preventing any internal condensation effect.
The apparatus according to the invention is characterized in that the inlet head comprises:
at least one orifice in the central part for insertion of the injector or of the spray nozzle,
a circuit for injection and heating of the vector gas rendered active simultaneously with injection of the liquid, the vector gas being directed to the vicinity of the injector or nozzle,
and cooling means for cooling the injector or nozzle, in particular by water or coolant flow or by air blowing.
According to one feature of the invention, the evaporation chamber contains deviation means arranged so that the distance covered by the droplets and vapours of the precursors is greater than the distance in a straight line between the nozzle of the injector and the outlet tube. The tube is subdivided into a plurality of elementary channels to increase the path and heating surface in the evaporation chamber. The tube can be made of metallic material, in particular stainless steel, or glass or quartz.
According to a preferred embodiment, the internal walls of the channels are covered with a chemically inert deposit, for example silicon carbide or tungsten, to prevent catalytic breakdown reactions of the vapours in contact with the metallic walls. Heating means surround the lateral surface of the tube coaxially and comprise resistances inserted in machined grooves arranged in two aluminium half-shells following exactly the same shape as the body of the evaporator so as to generate indirect heating of the tube. A first heating zone heats the upper flange and a second heating zone heats the tube and the lower flange, the temperature in each heating zone being controlled by a thermocouple.
According to one feature of the invention, each injector or spray nozzle has an individual cooling circuit, which is formed by an annular space filled with a coolant surrounding the body of the injector or spray nozzle.
According to another feature of the invention, a collar-piece extends up to the bottom face of the upper flange in the injection zone to minimize the surface accessible for backstreaming and condensation, the vector gas being injected into an annular volume arranged around the collar-piece where it expands and is heated before being reinjected into the space near to the nozzle of each injector or spray nozzle.